TPS65235-1: boost input voltage drop

Hi Toshiro,

My colleague will give you reply soon! 

BRs

Zixu

Hi Toshiro,

Thanks for reaching out. Could you please let us know customer's concern of this input voltage drop? Will this have an impact of their application? May I know the condition for this input voltage drop? Is it tested during start up, shutdown, or steady state, transient? Could you send us the waveform of Vin, Vout, SW and inductor current?

Thanks!

BRs

Lucia

Hi Lucia

What the customer is concerned about is the VIN voltage drop causes unexpected LNB output signal while 12.7VIN drop down to 12.4V for 10ms then returned, as shown in Yellow waveform in below. His test has done in steady state.

Actually he did not see any unexpected things though, this is just confirmation if you faced on issues in the past.

Did you experience any other issue in the past ?

Best regards,

Hi Toshiro,

Typically, for steady state operation, Vin voltage will not drop. What is the pink waveform represent for?

Thank!

BRs

Lucia

Lucia,

You will not need to care about pink, because this is not related to TPS65235-1.

The customer question is what kind of things will be expected to be happened in VLNB in case VIN transient of VIN=12.7V down to 12.4V then back to 12.7V in 10ms.

regards, 

Hi Toshiro,

If for steady state operation, Vin voltage will not drop if the input voltage is stable. During 10ms, is there other condition changes like the upstream devices?

Thanks!

BRs

Lucia

Hi Lucia,

no. there is no any other condition change except for 0.3V VIN transient.

regards,

Hi Toshiro,

Thanks for your feedback! We don't meet similar case before for steady state operation. Please let me clarify the test condition: Vin is set as 12.7V, VLNB is set as 19V. The load current always keeps the same. Where is the input voltage come from? If use a power supply for input, will the 0.3V drop still remain? Is there change for the VLNB voltage?

Thanks!

BRs

Lucia

Hi Lucia,

I am going to reply that your team has  hot experienced any issue.

Customer test condition

Vin=12.7V

VLNB=19V

Exact load current depends on TONE signal level though, this is negligible due to 19V VLNB bias voltage.

Power supply may came from SPMS power. Can you tell me reason you need this kind of information? Does any input power supply circuitry impact on VLNB output signal distortion or quality. Generally speaking, we know PSRR improves input voltage noise immunity and PSRR itself is significantly linked to open loop response.

When I checked the datasheet and Figure 13 presents the loop response at 10uH inductor case. Then it says approx.40db at 100Hz which is close to this application case. So I believe roughly 40dB PSRR is expected, which means the boost output voltage impacts on 1000 times lower than VIN input voltage noise. Now, we can assume 0.3V/1000 = 0.3mV voltage amplitude impact is expected on boost output. This number would be negligible against approx.600mV VLNB voltage swing.

Is my understanding correct ?

regards,

Hi Toshiro,

You are correct. 0.3V input voltage variation will have little influence on the LNB output voltage. The reason I ask whether it's from external power supply is because if the input supply is stable and work under steady state operation, we'll not see this change.

Thanks!

BRs

Lucia